Apparatus for cracking hydrocarbon oils



Nov. 29, 1932- A. E. HARNSBERGER ET AL. 1,889,199

PPRATUS FOR CRACKIN-G HYDROCARBON OILS I Filed 0013.50, 1929 o NN 2%@ www 'y UNITED STATES Patented Nov. a9, 1932 resales PATENT OFFICE AUDLEY'VE. HARNSBERGER AND CLYDE L. SMITH, OF CHICAGO, ILLINOIS, ASSIGNORS TO GYRO )PROCESS COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MICE- d IGAN APPARATUS FOR CRACKING HYDROCARBON OILS Application led ctober 30, 1929. Serial No. 403,583.

This invention relates to the art of cracking mineral oils and, more specifically, to .the production of oil/s of relatively low boiling point from oils of higher boiling points, and

wherein molecular decomposition of such higher boiling point oils takes place while the oils undergoing decomposition are 1n the vapor phase.

A. further object of the invention resides in providing for improved heat transmission to the vaporized oils undergoing molecular decomposition wherein said oils are heated in a uniform manner throughout substantially the entire body thereof and in such a mannerl as to avoid overheating of certain portions of the oil and underheating of other portions thereof. It has been found that there are certain optimum temperatures in the cracking of oil in the vapor phase which provide forl the most efficient operation, and the present invention provides for the passage of the oil vapors through the converter in such-manner as to secure the transmission of these optimum temperatures to the oil vapor ,l and to permit these temperatures to be maintained practically and relatively throughout the duration of the cracking operation.

For a further understanding of the invention reference is to be had to the following description andthe accompanying drawing kwherein z Figure 1 is a diagrammatic view illustrating conventional apparatus employed in carrying out the present invention,

Figure 2 is a vertical sectional view taken through the converter, and

Figure 3 is a transverse vertical sectional view taken through the converter.

Referring more particularly to the drawing, the numeral l designates a vaporizing furnace which in practice'partakes ofthe form of a pipe still and oil enters the vaporizing furnace by way of the pipe line 2 and is continuously forced by a pump 3 through the line 2 and the heating coil 4 arranged within the furnace 1. The internal temperature of the furnace is regulated so that the oil passing through the coil will be subjected to vaporizing temperatures but which temperatures will'be below temperatures which would be apt to produce material vcracking of the oil. ,From the coil 4 the oil is passed yinto an evaporator 5 where, due to the decreased pressure, a separation of the vaporous constituents of the oil takes place from the heavy liquid constituents. These liquid constituents collect in the bottom of the evaporator 5 and may be Withdrawn from the system by the pipe 6.

Leading overhead from the evaporator 5 is a pipe line 7 through which the vaporized fractions of the oil released from the evaporator are passed. These vapors are employedl as the cracking stock and it has been found des'rable, for purpose of minimizing carbon and coke deposit, to eliminate liquid entrainment in the vapors flowing from the evaporator to the cracking zone of the converter 8. In removing such liquid fractions or particles, the line 7 is equipped with a separator or liquid trap 9 which functions to'eject liquid en'trainment from the vaporized oils. The vapor outlet line 10 which leads from the separator to the converter terminates' in coils 11, the individual pipes of which possess an appreciable cross-sectional area to prevent high velocitf es of vapor flow through the coil.

The converter 8 comprises a furnace formed to ,include a setting 12 in which isl located a of the setting into combustion and tube chambers 14 and 15 respectively. The combustion chamber is provided with a burner 16 of 'sufficient capacity to develop the required converting temperatures Within the setting. Theheated gases pass from the top of the combustion chamber 14 over the bridge wall 13 and sweep downwardly through the heating -coils located in the tube chamber 15. The

furnace gases released `from the lower or cooler portion of the tube chamber may then be passed to the vaporizing furnace 1 for use in heating the oil passing through the coil 4. It will be noticed that the coil 11 is situated v in the zone of lower temperature of the tube dium and by this chamber 15 and sufficient heat ordinarily is absorbed by the oil vapors flowing through the coil 11 to raise the temperature of the oil from, for example, 7000 F. to 7500 F. The pipes comprising the coil 11 serve, therefore, as drying tubes in order to completely reduce to dry or vaporized form the oil stock prior to its introduction into the main zone of conversion. Y

rlhe outlet side of the coil 11 is connected with a pipe line 17 which leads to a manifold or header 18 arranged adjacent to the upper part of the converter. Connected with this header are parallel horizontally extending converter tubes 19. These tubes are of smaller diameter or cross-Sectional area than the tubes comprising the coil 11 andthe pipe line 17. The tubes 19 are disposed in the upper portion of the converter setting; and are positioned over the combustion and tube chambers 14 and 15. The entrance portions of the tubes 19 are thus disposed immediately over the combustion chamber 14 in order to receive radiant heat developed vthrough. the combustion of .fuels in the chamber 14 and to permit the radiant heat employed, to be utilized effectively in securing a rapid rise in the temperature of the oil vapors from an entering temperature of approximately 7 500 F. to temperatures in excess of 10000 F. ln fact, the oil vapors discharged from the rear ends of the tubes 19 possess a temperature of approximately 11000 F. to 11200 F., although these temperatures may vary between 10000 F. and 11500 F. Therefore, due to the small cross-sectional area of the tubes 19 and the consequent high Velocity of vapor flow therethrough and, furthermore, due to the location of the tubes 19 in the converter setting, a construction is provided permitting of rapid and effective heat transfer between the oil vapors and the `surrounding heating mearrangement the oil vapors are brought rapidly to a desired converting temperature with minimum deposition of coke or carbon or gas formation. Y

In order to secure the necessary time element to effect thorough conversion of the oil stock during its passage through the converter and yet to prevent overheating, on one hand and underheatin g on the other, the tubes 19 enter, at their discharge ends, into a second header 20 arranged parallel to the first header 18 and on the opposite side of the converter setting. The header 2O is connected by a pipe 21 of relatively large diameter, as regards the pipe 17, and leads to a bank of large size convertlng tubes 22, which are arranged in the tube chamber 15 above the coil 11.

Preferably, the flow of oil vapor undergoing conversion through the tubes 22 is eountercurrent to the flow of the furnace gases and this arrangement provides for a substantially uniform maintenance of converting temperature on the part of the oil vapors without material fluctuation. Due to the large cross-sectional area of the tubes 22, the velocity of vapor flow therethrough will be lower than that which obtains in the smaller parallel tubes comprising the first converter pass 19. lt will be observed that the flow of the vapor through the tubes 19 may be termed a multi-stream7 or parallel flow, whereas in the final conversion zone the flow takes place through the tubes 22 in series form, that is, progressively through the several tubes comprising the coil banlr` 22.

Converted vapors released from the bank 22 pass by way of a line 23 into a conversion arrester 24, and when the vapors enter the arrester they may possess a temperature varying between 10000 F. to 11500 F. ln the arrester the vapors are brought into direct physical contact with sulicient quantities of liquid cooling oil to secure an almost instantaneous reduction in the temperature of the oil vapor from conversion temperatures in excess of 10000 F. to non-reacting temperatures not in excess of 6000 F. looled oil is sprayed into the arrester from a. pipe line 25 which leads to a source of oil supply 20 wherein is contained the charging stock. The oil vapors released from the arrester pass into a fractionating tower 27 where the overhead vapors may be readily controlled. ,The vapors released from the top of the tower 27 may then be condensed as at 28 and led to a storage tank 29. The liquid the end point of I which collects in the bottom of the arrester 24 is passed to the bottom of the fractionating tower by way of the line 30, and the line 2 is connected with the bottom of the 'fractionating tower to force this liquid, which constitutes a charging stock, through the Vaporizing furnace, wherein the cycle of operation above given is repeated. y

Having thus described the invention, the distinctive features thereof may be summarized as follows:

First, the taking of a body of oil vapors and thoroughly drying the same by passage through a tube coil (11) located in a portion of the converting furnace where the heating medium is within 4000 F. or 5000 F. of the temperature of the oil vapor at the time the vapor enters the tube coil, therebf,r insuring a mild condition of low furnace temperatures on the drying tubes even though the latter should beeomepartially filled with coke or carbon due to the drying process. Since the tubes comprising the coil 11 are of large area the formation of coke on the walls thereof does not interfere with sustained operation of the converter since, due to the provision ofthe evapora-tor 5 and the trap 9, but small quantities of liquid reach the drying tubes and then, due to the cross-sectional area of such tubes, the carbon deposit therein does not attain a. thickness sufficient to interfere materially with the oil vapor flow through the tubes for effecting heat transfer between the oil vapor and the internal heating medium. i

Second, the invention provides for the dividing of the single dry stream of oil vapor into a number of parallel or multiple smaller streams, which is accomplished by the provision of theheader 18 and the converting tubes 19. Within these latter tubes the ratio of surface-to-volume is increased in order to effect rapid heating of these dry vapors to a cracking temperature, which is accomplished by exposing these multi-streams of oil vapor to a high degree of radiant heat and this is accomplished Without permitting any one stream to crack beyond a point of maximum efficiency and We preferably limit the cracking in the tubes 19 to less than 25 per cent of the total cracking performed in the converter. i

Third, by recombining these multi-vapor streams into one stream-by the employment of the pipe 21, 'We thereby bring about a condition Where the entire mass of the vapor is brought to the same temperature, although for various reasons the temperature of the oils in passing through the different tubes 19 may vary in one tube with respect to the others. The recombined stream of oil vapor is then exposed t0 a moderate degree of radiant and convection heat in the furnace setting, and the location of the coil 22 in said setting is such as to permit of the supplying to the oil vapor of that quantity of heat made necessary by the endothermic conversion reactions, and at the same time holding the vapors at this point at substantially a constant temperature.

The advantages of the above construction and system of operation are many. In operation, in the case of a 1000 barrel converterl the vapors normally enter the 10 inch drying tubes 11 located in the base of the converter, the entering temperature of the vapor being approximately 700 F. and the exit temperature 740 F. to 750 F., These vapors are then conducted to the front of the converter over the fire box zone and split into approximately small streams comprising the tubes 19. At the end of this top row of tubes the header 20 is provided which conducts the vapors into the single pipe line 21 of approximately 12 inches in diameter, and from the pipe line 21 the oil vapors pass through the bank of tubes 22 also composed of 10 inch tubes and which are so arranged-in the furnace setting as to maintain the converting temperature of the oil vapors.

In prior systems the small tubes are continued in the tube chamber with the result that the vapor flows in a plurality of streams of small cross-sectional area through the entire converter, just as We provide for the first pass of the converter. It is our thought that the reason such prior systems do not obtain' high conversions and consequent high gasoline yields is that the degree of cracking in each of these multiple streams vary somewhat being too great in certain streams or passes and insuiicient in others, and that, therefore, the results obtained are a composite of under-cracking and over-cracking. It has been observed that with such prior systems which operate at high temperatures in order to crack .hard enough to secure high gasoline yields, there results in considerable overcracking on some of the vapor streams, which produces too large quantities of fixed gas to make such an operation economically feasible and, conversely, if the temperatures are too low the gasoline yield falls and the per centage of recovery of gasoline is too low for economical operation. Thus, to overcome these conditions the present invention resides in recombining the multi le streams after their passage through the rst portion of the converter into a single stream, wherein a uniform he'atingof all portions of the oil vapor takes place. v

The reason that one large tube is not used throughout the converter is attributable to the fact that such a tube in order to secure suliicient heating surface would have to be very long, and further, in order tov secure heat transfer, would require a high vapor velocity which would result in dctrimentally high frictional back pressures. By dividing the vapor stream into a large number of small streams for passage through the high radiantheat zone the surface-to-volume ratio is very, greatly increased. For instance, one 12 inch pipe is equivalent to 16 three inch pipes in cross-sectional area and with a given vapor flow either would have the same vapor velocity. However 16 three inch pipes have approximately 121/2 square feet of heating sur'- face available per foot of length or four times as much heating surface as one 12 inch pipe, which has only three and one-half square feet of heating surface per linear foot. However, at the end of the lirst pass 19 the converter is operated so that the vapor temperature may be approximately l100 `F. and, therefore, since most of the heating is done We are then permitted to recombine the multistreams into one large stream and Without difficulty secure a sufficient heating surface to supply the loss of heat due to the endothermic cracking reaction, and yet limit the exposure of the oil vapors to said converting temperatures for the proper period of time necessary to secure the most eflicient results.

What is claimed is:

1. An oil converter comprising an enclosing Wall structure, a vertical bridge extending transversely of said wall structure and dividing the latter internally into combustion and tube chambers, said chambers communicating relatively over said bridge Wall, a row of horizontally extending parallel tubes supported by said wall structure and disposed openly in the upper portion of said converter over said combustion and tube chambers and providing for parallel flow of oil vapor in a multiplicity of similarly moving adjacent streams, a header connected with the entrance ends of said tubes, a bank of serially connected tubes disposed in said tube chamber and connected with the discharge ends of said parallel tubes, said serially connected tubes possessing a greater cross sectional area than any one of said first-named parallel tubes, combustion developing means situated in said combustion chamber for producing furnace temperatures within said converter suficiently high to heat oil vapors passing through said tubes to desired conversion temperatures, anda third bank-of tubes disposed in the low ^temperature zone of said tube chamber, the discharge side ofsaid third bank of tubes being connected with said header.

2. An oil converter comprising a refractory wall structure, a bridge disposed within said Wall structure and extending transversely thereof to divide the interior of the converter into combustion and tube chambers, said chambers communicating over the top of said bridge, combustion developing means disposed in said combustion chamber, a plurality of horizontally arranged parallel tubes supported by said Wall structure in the upper portion of the converter and extending openly over said combustion and tube chambers said tubes providing for parallel flow of oil vapor therethrough in a multiplicity of similarly moving adjacent streams, aheader disposed exteriorly of said wall structure and connected with the vapor inlet ends of said tubes, a plurality of seriallyconnected tubes arranged in said tube chamber immediately below said parallel tubes, connections between the discharge ends of said parallel tubes and said serially connected tubes, said serially connected tubes possessing a greater cross sectional area than the individual-parallel tubes, a plurality of drying tubes disposed in said tube chamber below said serially connected tubes, means for delivering substantially vaporized oils to said drying tubes, and pipe means connecting the discharge side of said drying tubes with said header.

3. An oil converter comprising a refractory wa ll structure, a bridgedisposed within said 'Wall structure and extending transversely thereof to divide the interior of the converter into combustion and tube chambers, said chambers communicating over the top of said bridge, combustion developing means disposed in said combustion chamber, a plurality of horizontally arranged parallel tubes supported by said Wall structure in the upper portion of the converter and extending openingly over said combustion and tube chambers said tubes providing for parallel flow of oil vapor therethrough in a multiplicity of similarly moving adjacent streams, a header disposed exteriorly of said wall structure and connected With the vapor inlet ends of said tubes, a plurality of serially connected tubes arranged in saidtube chamber immediatelybelowsaidparallel tubes, connections between the discharge ends of said parallel tubes and said serially connected tubes, said serially connected tubes possessing a greater cross sectional area than the individual parallel tubes, a plurality of drying tubes disposed in said tube chamber below said serially connected tubes, means for delivering substantially vaporized oils to said drying tubes, )ipe means connecting the discharge side of said drying tubes with said header, said combustion developing means serving to heat and maintain the vaporized oils passing through the parallel and serially connected tubes at temperatures in excess of 1000o F. and to heat the vapors passing through the drying tubes to a non-cracking temperature sufliciently high to eliminate liquid entrainment in such vapors.

In testimony whereof We Aaflix our signatures.

AUDLEY E. HARNSBERGER. CLYDE L. SMITH.

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